Organic Carbon Distributions in Shallow Soils of Pinyon‐Juniper Woodlands

Abstract

AbstractProperties of soils associated with pinyon (Pinus edulis Engelm.)‐juniper (Juniperus spp.) communities of the western USA reflect a mosaic of canopy and interspace environments. This study was initiated to examine the influence of these contrasting environments on organic carbon (OC) distributions and associated soil properties of shallow soils in a pinyon‐juniper woodland of east‐central Utah. The mosaic of interspace and canopy environments results in a complex of soils with two distinct OC distribution patterns. In both interspace and canopy soils, color values and root distributions are related to measured OC. Tree roots are concentrated just above the lithic contact in transitional R/A and Cr/A horizons in all soils. Decay of this root material represents the dominant organic‐matter input to interspace soils, which are essentially devoid of vegetation and lack O horizons. As a result, OC increases with depth and the highest OC contents and darkest soil colors are found in R/A and Cr/A horizons of these soils. Canopy soils also have relatively high OC contents just above lithic contacts but contain maximum OC and darkest soil colors in A1 horizons underlying litter layers. All soils exhibit increases or irregular decreases in OC with depth and have similar distribution patterns for total N and NaHCO3‐extractable P. The OC distribution patterns result in inappropriate classification of some of these shallow upland soils as Fluvents according to the U.S. soil taxonomy.